DE1920294A1 - Process for the continuous, chemical deposition of nickel coatings containing boron - Google Patents

Description

COLOR FACTORY BAYERAG

2 April 1, 1969

GB / Schr Pitent Department

Process for the continuous, chemical deposition of coatings containing boron

Electroless nickel plating baths for producing boron-containing nickel coatings on metal surfaces are known. After German Auslegeschrift I.I37.9I8 contain alkaline ^

chemical nickel-plating baths, which with the reducing agent -

Sodium boranate, a nickel salt (chloride), Ethylenediamine as a complexing agent and sodium hydroxide. the The rate of reduction and the reduction yield of chemical nickel plating can according to the German Auslegeschrift 1.25 ^ .935 can be increased by adding at least one compound of an element from groups II to VI of the periodic table.

In the German Auslegeschrift 1.237 * 399, a process for continuous chemical nickel plating has also been described. The nickel salt concentration in alkaline electroless nickel-plating baths is maintained during nickel-plating M by continuously adding an aqueous solution of nickel chloride with a complexing agent which has a lower boiling point than the complexing agent contained in the nickel-plating bath. The reducing agent concentration and the alkali content of the bath are kept constant during the electroless nickel plating by continuously adding a sodium-alkaline sodium boronate solution.

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However, these baths have the disadvantage that the complexing \ ~ z formers for the nickel salt replenishment solution. '' - an enrichment of the complexing agent and thus a decrease in the deposition. to avoid conversion rate and the reduction yield during continuous electroless nickel-plating - must have a lower boiling point than the operating temperature of the bath. When ammonia or low-boiling, water-soluble amines are used as complexing agents for the nickel salt supplement solution, suction devices to be designed accordingly are required for a continuously operated electroless nickel-plating system. Another disadvantage of the known process is the relatively poor solubility of the nickel chloride-ammonia complex (approx. 5 to 4 dm / l) is only partially permitted, since the sum of the supplementary solutions does not generally correspond to the evaporation losses during the continuous electroless nickel plating.

These disadvantages can be avoided if a Both complexing agent-free and concentrated nickel chloride solution to be entered continuously in the electroless nickel plating bath.

It has been now found a process for the continuous, chemically depositing "found an alkaline aqueous bath, wherein the nickel salt, alkali borohydride, Ä'thylendiamin, alkali metal hydroxide and Stabl" of boron-containing nickel coatings using - ^FIC lisa factors containing bath is operated in circulation and the 'spent Chemicals are supplemented, characterized

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that supplementing the nickel salt with an aqueous nickel salt solution through continuous introduction into the turbulent flow of a branch flow cooled to below 70 ° C the circulated bath liquid takes place.

The solutions required to maintain the alkali, reducing agent and stabilizer concentration can also be metered into the cooled branch stream in the form of a sodium-alkaline alkali boronate solution and an aqueous stabilizer solution Alkali boranate content can be refreshed again with an aqueous complexing agent-free nickel chloride solution at a bath temperature of approx. 70 ° C. if the concentration is carried out by introducing an aqueous nickel chloride solution into a turbulent bath flow. For example, it is possible to drop a bath containing 5 g / l nickel chloride hexahydrate, 60 g / l ethylenediamine, 40 g / l sodium hydroxide in a mixing vessel with a breakwater and propeller stirrer at 70 ° C., which is depleted in nickel ions of 71.5 ml of an aqueous solution of 550 g / l NiClp. 6 HpO back to the initial concentration of 50 g / l NiCl ₂ . 6 HpO to be discontinued. Under these conditions, the addition of aqueous nickel chloride solution without precipitation of basic nickel salts or finely divided nickel-boron precipitates (wild decomposition) up to a nickel chloride concentration of approx. 60 g / l NiClp. 6 HpO can be carried out in an alkaline nickel-plating bath. The possibility of using the bath up to a content of 60 g / l NiCl ₂ . Refresh 6 H ₃ O, where on 1 mol of NiCl ₂ approximately 4 moles Sthylendiamin come allowed to keep in a continuously operated Vernickelungsanlage the circulating volume of from about 90 ⁰ C to about 70 ° C to be cooled split stream low.

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The continuous refreshing of a nickel-plating bath by introducing an aqueous, complexing agent-free nickel salt solution into a mixing system connected to the hot Ural River is only possible at very high flow rates. In this way it is possible to obtain 150 g / l NiCl _{2 of} an aqueous nickel salt solution in a 50 l bath with a circulation of 900 l / h. 6 contains HpO, to be introduced into the nickel-plating bath via a mixed system, but lower circulation speeds or higher nickel salt concentrations lead to a wild deposition of nickel-boron compounds. ·

The principle of a technical, continuously operated nickel-plating plant according to the invention is based on the following the figure 1 described:

Made from austenitic Cr-Ni steel, electrically has isolated Verniekelurigswanne (1) a sloping floor, with the drain located at the lowest point of the floor. Inlaid or hung and with A heating coil made of the same material is conductively connected to the bath tank. The nickel plating bath is heated with steam or indirect heating, e.g. B. with oil. The heating coil can also be used as a cooling element - e.g. B. by passing it through of water or cold brine - to cool the nickel-plating solution can be used after the nickel plating is finished. The container wall, the counter electrodes (2 and 2a) and the Reference or measuring electrodes (5 and yes) are with a control device (4) connected. Anodic polarization prevents the bath tank (1) and the heating elements from being nickel-plated (German patent specification 1,277,642 and Belgian patent specification 692,059). An edge suction system attached to the edge of the container ensures that no exhaust gases produced during chemical nickel plating get into the room. The container wall is

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insulated against heat radiation. A movement of the nickel-plated Objects ensures the exchange of the nickel plating solution on the metal surfaces to be nickel-plated. The nickel-plating solution flows through the drainage port during electroless nickel-plating the tub is continuously pumped over by a pump (5) and a filter (6 and 6a). A pump (7) is the Circulation removed a branch stream, which is cooled in a heat exchanger (8) from 90 ° C to 60 to 70 ° C, via a flow meter (9) and circulated via a mixing system (10), is fed back. A metering pump is used to supply the cooled branch flow with the chemical nickel-plating process Amount of stabilizer solution (11) added continuously. The entry of the aqueous nickel chloride solution (12) takes place in the Mixed system (10). The alkaline reducing agent solution (13) can be fed into the cooled branch stream behind the mixing system (10) or continuously metered into the circuit upstream or downstream of the filters (6 and 6a) of the alkaline nickel-plating bath. The mixing system (10) consists of a cylindrical container with the diameter D and four inserted baffles, whose width is 1/10 of the container diameter. A propeller stirrer was used as the stirrer. The speed of the stirrer is * 1000 to? 000 rpm.

The currentless, continuous nickel-plating by means of enrollment a complex agent-free metal salt supplement solution compared to the known method of adding a complex agent-containing nickel salt supplement solution, the following advantages: A complex agent-free nickel salt supplement solution can according to the present invention in significantly higher concentrations can be added to the alkaline nickel-plating bath. This has a number of advantages:

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Compared to the previously known method in which ammoniacal Nickel salt solutions are used for refreshing, the inventive method requires less energy, since no water and ammonia need to be evaporated. The performance of the suction devices can also be significantly weaker be interpreted. In addition, the suction device does not have to be equipped with a separator for ammonia. Finally, adding the relatively highly concentrated nickel salt supplement solution increases the need for nickel of the continuously operated bath covered without increasing the volume of the bath, so that the deposition rate or the surface volume ratio can be increased in the nickel plating.

Example i

In a system for electroless nickel plating according to the figure, 50 1 standard bath solution of the composition

30 g / l of nickel chloride hexahydrate

60 g / l ethylenediamine (98 #ig)

40 g / l sodium hydroxide
0.5 g / l sodium fluoride
0, ^ g / l sodium boranate

30 mg / l lead acetate

heated to the nickel-plating temperature of 90 ° C * The chemical The nickel-plating solution is continuously fed through the drainage port of the tub via a pump (5) or the filter (6 and 6a). A pump (7) is used to circulate Branch flow of 10 l / h removed. This is cooled from 90 ° C to 60 ° C in a cooling system (8) using a flow meter (9) and circulated via a mixing system (10)

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fed back. The mixing system (10) consists of a cylindrical vessel (D = 10 cm, drainage height 10 cm) with four inserted baffles, the width of which is 1/10 of the vessel diameter. A propeller stirrer with 2000 rpm is used as the stirrer. The nickel-plating system is anodically protected against chemical nickel-plating by means of a potentiostatic control device (4), the measuring electrodes (3 and J5a) and the counter electrodes (2 and 2a). After known pretreatment (degreasing, pickling, rinsing), the metal parts to be nickel-plated are suspended in the nickel-plating tub. The total surface of the parts to be nickel-plated is 50 dm ² (0 / V = 1 dm ² / l). Downstream of the flow meter (9) in the cooled branch stream (11), 626 ml / h of stabilizer solution containing 2 g / l of lead acetate are introduced. 784 ml / h of an aqueous nickel salt replenishment solution containing 200 g / l NiCl ₂ are continuously introduced into the mixing vessel (10). 6 contains H ₂ O. The nickel chloride concentration behind the mixing system (10) may be 60 g / l NiCl ₂ . Do not exceed 6 H _{3 O.} The nickel chloride concentration in the branch stream upstream and downstream of the mixing system can be controlled photometrically. In the main stream, e.g. B. at (13) or behind the filters (6 and 6a) one enters continuously 500 ml / h of a sodium boronate solution containing 52.5 g / l NaBH ^ and 100 g / l NaOH. Every hour 39 x 25 g nickel-boron alloy are deposited on the parts to be plated. This corresponds to a deposition rate of 9 * 6 / µm _{/ h (ρ Ν ._ β} = 8.2 g / cnr).

Example 2

50 l of a chemical nickel plating bath of the composition

18.2 g / l nickel chloride hexahydrate 39 * 0 g / l sodium hydroxide

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62.8 g / l ethylenediamine

0 * 4 g / l sodium boronate

100 mg / l arsenic acid

24 mg / l thallium sulfate

are heated in a system as described in Example 1 to the nickel-plating temperature of 90 ° C and operated continuously at a surface-volume ratio of the metal parts to be nickel-plated of 1 dm / l. The circulating a branch current of 15 is / removed h l, which is cooled in the cooling system (8) of 9O ⁰ C to 55 ° C. In the cooled branch stream, 250 ml / h of an aqueous thallium sulfate solution containing 8 g / l Tl ₃ SO ^ are continuously introduced at (11). _{86O ml / h of a nickel salt supplement solution containing 350 g / l NiCl 3} is continuously introduced into the mixing system (10) at a stirring speed of 2000 rpm. Contains 6 H _{3 O.} 314 ml / h of a tin chloride solution containing 8 g / l SnCl ₃ are also continuously introduced into the mixing system. 2 H ₃ O and 27 g / l NaOH. 724 ml of a sodium boronate solution containing 52.5 g / l NaBH ₁ ^ and 90 g / l NaOH are metered in continuously behind the filters (6 and 6a). Every hour, 74.4 g of nickel-boron alloy are deposited on the parts to be nickel-plated (50 dm surface). This corresponds to a deposition rate of 18.1 _{/ µm / h (p N} 4 g = 8.2 g / cnr). Precipitation of basic nickel salts or nickel borides in the nickel-plating solution was not found.

example 7>

In a 50 1 plant, as described in Example 1, the chemical nickel plating is carried out with an S / V ratio of 1 dm / l and an operating temperature of 90 ° C. The composition of the bath is:.

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21.0 g / l nickel chloride hexahydrate

40.0 g / l sodium hydroxide

63 * 2 g / l ethylenediamine

0.45 g / l sodium boronate

18O rag / l o-arsenic acid

30 mg / l thallium sulfate

To introduce the nickel salt supplement solution, a branch stream of 15 l / h is withdrawn from the circulation, which is cooled from 90 ° C. to 60 ° C. via a cooling system (8) and in which 9βθ ml / h of an aqueous thallium sulfate solution containing 7.8 g / l Tl ₂ SO ^ contains, enters continuously. In. the mixing system carries one continuously 1380 ml / h of a nickel salt solution, the 35Ο g / l NiCl-. 6 HpO contains. 1050 ml / h of a reducing agent solution containing 58 g / l NaBH ₁ and 130 g / l NaOH 'are continuously metered into the circulation behind the filter (6 and 6a).' Every hour, 128 g nickel-boron alloy are deposited on the parts to be nickel-plated (50 dm surface). The deposition rate is 31 * 2 / µm / h. In this case, too, no precipitation of basic nickel salts or of nickel borides in the nickel-plating solution could be found.

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Claims (3)

Patent claims: (I)) Process for the continuous, chemical deposition of boron-containing nickel coatings using an alkaline aqueous bath, the bath containing the nickel salt, alkali boronate, ethylenediamine, alkali hydroxide and stabilizers
is operated in circulation and the chemicals used are supplemented, characterized in that the supplement of the
Nickel salt with an aqueous nickel salt solution by continuously introducing it into the turbulent flow of a
takes place below 70 ° C cooled Zxveigstromes of the circulated bath liquid. 2) Method according to claim 1, characterized in that as a nickel salt supplement solution aqueous nickel chloride solutions Concentrations of 100 to 600 g / l can be used. 3) Method according to claim 1 and 2, characterized in that
that the nickel chloride content in the cooled branch stream after the addition of the nickel salt supplement solution is from 20 to 60 g / l NiCl ^ .ö H ₃ O. Le A 12 201 - 10 - 009846/1 A A 3